Section 13.2

Using Gas Laws to Solve Problems

Section 13.2

Using Gas Laws to Solve Problems

1. To understand the ideal gas law and use it in calculations

2. To understand the relationship between the partial and total pressure of a gas mixture

3. To do calculations involving Dalton’s law of partial pressures

4. To understand the molar volume of an ideal gas

5. To learn the definition of STP

6. To do stoichiometry calculations using the ideal gas law

Objectives

Section 13.2

Using Gas Laws to Solve Problems

A. The Ideal Gas Law

• Boyle’s Law V = k (at constant T and n) P

• Charles’s Law V = bT (at constant P and n) • Avogadro’s Law V = an (at constant T and P)

We can combine these equations to get

Section 13.2

Using Gas Laws to Solve Problems

A. The Ideal Gas Law

Rearranging the equation gives the ideal gas law:

PV = nRTR is a constant = 0.08206 L atm

mol K

Note the units that are used with this constant

Section 13.2

Using Gas Laws to Solve Problems

The Combined Gas Law

Ideal Gas Law: PV = nRT

P1V1 = nRT1 or P1V1/T1 = nR

P2V2 = nRT2 or P2V2/T2 = nR

Combined Gas Law: P1V1/T1 = P2V2/T2 (for a constant number of moles)

Section 13.2

Using Gas Laws to Solve Problems

• What value do we measure for the pressure of a gas as we mix different gases in a container?

B. Dalton’s Law of Partial Pressures

Dalton’s law of partial pressures

• For a mixtures of gases in a container, the total pressure exerted is the sum of the partial pressures of the gases present.

• Ptotal = P1 + P2 + P3 + …….

Section 13.2

Using Gas Laws to Solve Problems

B. Dalton’s Law of Partial Pressures

• The pressure is independent of the nature of the particles.

• The pressure of the gas is affected by the number of particles.

Section 13.2

Using Gas Laws to Solve Problems

Two crucial things we learn from this are:

B. Dalton’s Law of Partial Pressures

• The volume of the individual particles is not very important

• The forces among the particles must not be very important

Section 13.2

Using Gas Laws to Solve Problems

Collecting a gas over water

B. Dalton’s Law of Partial Pressures

• Total pressure is the pressure of the gas + the vapor pressure of the water.

Collecting Hydrogen

Section 13.2

Using Gas Laws to Solve Problems

Collecting a gas over water

B. Dalton’s Law of Partial Pressures

• How can we find the pressure of the gas collected alone?

Section 13.2

Using Gas Laws to Solve Problems

Molar Volume

C. Gas Stoichiometry

• Molar volume of an ideal gas at STP = 22.4 L

• Standard temperature and pressure (STP)– 0oC and 1 atm

• For one mole of a gas at STP, what is the volume?